CAIE A-Level Chemistry 17 Carbonyl Compounds

Practise aldehyde and ketone preparation, reactions, qualitative tests and nucleophilic addition at C=O.

[Maximum number: 8]

$4\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCHO}$ is used in the synthesis of some antibiotics.

(a)

Two reaction sequences are shown.

Figure for Question (a) — CAIE A-Level Chemistry AS

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(i)

Reaction 1 is an oxidation reaction.

Identify the reagent(s) and conditions for reaction 1.

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(ii)

Give the balanced equation for the reaction of $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCHO}$ with $\mathrm{NaBH}_{4}$ to form S.

Use [H] to represent an atom of hydrogen provided by $\mathrm{NaBH}_{4}$ .

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$\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCHO}+2[\mathrm{H}] \rightarrow\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}_{2} \mathrm{OH}$

(b)

X, Y and Z are all isomers of $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCHO}$ .

A summary of some of the reactions and properties of X, Y and Z is shown in the table.

Table for Question (b) — CAIE A-Level Chemistry AS

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(i)

X and Y each contains a carbonyl group.

Complete the table with the expected observations for the reactions of X and Y with 2,4-DNPH.

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(ii)

Identify the functional group present in Y that causes the recorded observation with Fehling's solution.

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(iii)

X contains a carbonyl group. X reacts with HCN , in the presence of a small amount of NaCN , to form $\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{C}(\mathrm{OH}) \mathrm{CN}$ as shown.

\mathbf{X}+\mathrm{HCN} \rightarrow\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{C}(\mathrm{OH}) \mathrm{CN}

Draw the mechanism of the reaction of X with HCN .
- Draw the structure of X and the intermediate.
- Include all charges, partial charges, lone pairs and curly arrows.

Figure for Question (iii) — CAIE A-Level Chemistry AS

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Figure for Answer to Question (iii) — CAIE A-Level Chemistry AS

M1: Correct structure of X and correct dipole on C=O

M2: curly arrow from C=O bond to O AND intermediate with CN attached and -ve charge on the O

M3: curly arrow from lone pair on $\mathrm{CN}^{-}$ to C(=O) in X AND curly arrow from lone pair in the intermediate to $\mathrm{H}^{+}$

(iv)

State the role of NaCN in the reaction in (c)(vii).

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Covered syllabus points

17. Carbonyl compounds question 1

Question (a)

Question (i)

Question (ii)

Question (b)

Question (i)

Question (ii)

Question (iii)

Question (iv)